1. Field of Invention
This invention relates to resin bonded sand molds and in particular to a system and process for reducing casting pollution, recovering a portion of the molding sand for reuse, producing a low BTU fuel gas by partial combustion of the bonding resin, and recovering a portion of the casting heat.
2. Description of the Prior Art
Heretofore, current foundry practice employing no-bake molds and cores have ventilation and sand reclamation operations. Organic waste products are removed from molds and cores in dry scrubbers and transported to dumping sites for disposal. The scrubbed sand is returned for reuse. At the present time there is no practical use for recovered binder residues. Care must be exercised in disposing of organic waste products, since they pose a potential problem for the environment.
Present ventilation systems include the dilution of foundry air with large quantities of unpolluted air and removing the same from the foundry by forced air and/or induced air systems. The air removed from the foundry is exhausted into the outside atmosphere where air standards are still lenient enough to permit such operation. The existing systems must move huge quantities of air and are therefore expensive to install and maintain operation thereof. Additionally, extra fuel is required to preheat the make-up air for the foundry operation.
Under normal foundry practice, large quantities of dust can be present in the foundry environment. This is particularly true in the areas devoted to pouring and shakeout operations. As stated in a volume of the American Society for Metals Handbook, silica dust can produce silicosis if there is sufficient exposure, in terms of time and concentration, to free crystalline silica dust of a particle size below five microns. When silica dust concentrations greatly exceed the maximal allowable, a case of silicosis can develop in two to twenty years, the average being ten years.
In nobake molding practices employing organic sand binders environmental affects must be considered for products of the thermal decomposition of the organic binders. The smoke and thermal decomposition products require control equipment. Thermal decomposition products include, but are not limited to, carbon monoxide, carbon dioxide, nitrogen, hydrogen, methane, formaldehyde, ammonia, hydrogen cyanide, acetylene, ethane, paraffin hydrocarbons, aromatic organic compounds, and the like.
The three major sand reclamation systems currently available to foundrymen using nobake sands are thermal, wet and dry scrubbing. Thermal reclamation is the most expensive to install and operate, but produces the cleanest reclaimed sand. A thermal reclaimer requires in the order of 1.5 million BTUs of heat per ton of sand treated, or 4.5 million BTUs per ton of metal cast, at a 3:1 sand to metal ratio to remove up to 96 percent of the organic binder residues from any organic nobake sand mold system. The thermal reclamation system is seldom employed in the industry.
A wet reclamation system is less expensive to operate than a thermal reclamation system, but more expensive than a dry scrubbing system. A wet reclamation system will remove from 35-45 percent of the organic binder residue from the used nobake nobake molding sand. However, the sludge byproduct of the wet reclamation operation requires an environmentally safe disposal site.
A dry scrubber system is the least efficient system to reclaim used nobake foundry sand, its efficiency being in the order of removal of from 25-35 percent of the binder residues from the sand processed for a shotblast type dry scrubber. This process is employed most often because of its low installation cost.
In the dry scrubber system of reclamation, the sand is crushed and its surface abraded resulting in up to 20 percent of the sand being processed being lost because of "dust losses". The wet reclamation system has a less severe "dust loss" problem and the thermal system has the least "dust loss" problem.
The binder residues removed by the sand reclamation system have no practical use at this time, and their disposal method is dumping.
In my copending patent application Ser. No. 130,256 filed on Mar. 14, 1980 and issued as U.S. Pat. No. 4,325,424 I teach a mold system and process for nobake casting mold assemblies which overcome many of the deficiencies found in the prior art. A vacuum source means induces ambient foundry air to flow through the mold into a vacuum plenum member. A low BTU gas comprising gas products and condensate matter is evolved from the mold into the plenum member. Combustion air may be mixed with the collected gas products and condensate matter to form a combustible mixture. The combustible mixture may be burned to preheat combustion air as required, produce hot water, and enable one to heat treat castings in the mold assemblies.
An object of this invention is to provide a new and improved system and process for casting metals in nobake sand molds.
Another object of this invention is to provide new and improved apparatus and process for reducing air pollution in foundries employing nobake sand molds.
A further object of this invention is to provide a new and improved apparatus for causing air to flow through selected regions of a nobake mold to thermally decompose the organic binder therein to produce a gas having a low BTU content.
A still further object of this invention is to provide a new and improved system for insitu thermal recovery of sand from a nobake sand mold, producing a gas therefrom that has a low BTU content which is storable or can be used in several ways for preheating air and/or water, for providing heat as required in the foundry.
Another object of this invention is to recover the casting heat from the casting during the cooling cycle.